Recessed light fixtures (also known as “canister” fixtures) and flush-mount electrical boxes (also known as “junction” boxes) are commonly used in indoor and outdoor downlight applications. Examples of industry standard can-canister fixtures are illustrated as fixture 800 at FIG. 8 and fixture 900 at FIG. 9. Examples of industry standard junction boxes are illustrated as boxes 1000, 1100, and 1200 at FIGS. 10, 11, and 12, respectively. Both canister fixtures and junction boxes may be installed in a hollow opening in a ceiling or other surface. Canister fixtures commonly feature a lamp socket configured to receive an incandescent lamp or compact fluorescent lamp (“CFL”).
Both incandescent and fluorescent lamp types suffer from certain disadvantages. For example, incandescent lamps convert approximately 3% of electrical power consumed into usable light, while the remaining 97% of power may be wasted as heat. Compared to an incandescent lamp, a fluorescent lamp converts electrical power into useful light more efficiently, delivers a significantly longer useful life, and presents a more diffuse and physically larger light source. However, fluorescent lamps are typically more expensive to install and operate than an incandescent lamp because of the requirement for a ballast to regulate the electrical current. Many fluorescent lamps have poor color temperature, resulting in a less aesthetically pleasing light. Also, if a fluorescent lamp that uses mercury vapor is broken, a small amount of mercury (classified as hazardous waste) can contaminate the surrounding environment.
Digital lighting technologies such as light-emitting diodes (LEDs) offer significant advantages over legacy lamps. These advantages include, but are not limited to, better lighting quality, longer operating life, and lower energy consumption. Consequently, LED-based lamps increasingly are being used not only in original product designs, but also in products designed to replace legacy lamps in conventional lighting applications such as canister-based downlights. However, a number of installation challenges and costs are associated with replacing traditional lamps with LED illumination devices. The challenges, which are understood by those skilled in the art, include light output, thermal management, and ease of installation. The costs, which are similarly understood by those skilled in the art, typically stem from a need to replace or reconfigure a canister fixture configured to support traditional lamps to support LEDs instead.
By the very nature of their design and operation, LEDs have a directional light output. Consequently, employing LEDs to produce light distribution properties approximating or equaling the light dispersion properties of traditional lamps may require the costly and labor-intensive replacement or reconfiguration of the host light fixture, and/or the expensive and complexity-introducing design of LED-based solutions that minimize the installation impact to the host light fixture. Often material and manufacturing costs are lost in this trade off. Also, light distribution design choices such as large parabolic reflectors and multiple optics operate contrary to the objective of presenting a low profile lighting device as fully assembled.
Another challenge inherent to operating LEDs is heat. Thermal management describes a system's ability to draw heat away from an LED. Passive cooling technology, such as a heat sink thermally coupled to a digital device, may be used to transfer heat from a solid material to a fluid medium such as, for example, air. LEDs suffer damage and decreased performance when operating in high-heat environments. Moreover, when operating in a high-temperature ambient environment and/or a space-limited enclosure, the heat generated by an LED and its attending circuitry can cause damage to the LED. Heat sinks are well known in the art and have been effectively used to provide cooling capacity, thus maintaining an LED-based lamp within a desirable operating temperature. However, heat sinks can sometimes negatively impact the light distribution properties of lighting solution, resulting in non-uniform distribution of light about the fixture. Heat sink designs also may add to the weight and/or profile of an illumination device, thereby complicating installation, and also may limit available space for other components needed for delivering light.
Replacement of legacy lighting solutions may be complicated by the need to adapt LED-based devices to meet legacy form standards. For example, in a commercial lighting system retrofit, disposal of a replaced lamp's fixture housing often is impractical. Consequently, retrofit canister downlights often are designed to adapt to a legacy housing, both functionally and aesthetically. Also, power supply requirements of LED-based lighting systems can complicate installation of LEDs as a retrofit to existing light fixtures. LEDs are low-voltage light sources that require constant DC voltage or current to operate optimally, and therefore must be carefully regulated. Too little current and voltage may result in little or no light. Too much current and voltage can damage the light-emitting junction of the LED. LEDs are commonly supplemented with individual power adapters to convert AC power to the proper DC voltage, and to regulate the current flowing through during operation to protect the LEDs from line-voltage fluctuations. The lighting industry is experiencing advancements in LED applications, some of which may be pertinent to improving the design of low profile canister downlighting solutions.
U.S. Pat. No. 7,178,946 to Saccomanno et al. discloses a luminaire device that includes a tubular fluorescent bulb that is partially surrounded on an underside by a curved reflector. Light rays from the bulb are directed towards the curved reflector and reflected towards a collimator. A light guide featuring a refractive slab captures the light output from the collimator and redirects the light away from the device in a uniform luminance. However, employing legacy lamp technology may result in a design that suffers light losses (both to reflection and to absorption).
U.S. Pat. No. 8,328,406 to Zimmerman is directed to an illumination system that employs a discrete light source, a reflector, and first and second substantially flat light guides. This lighting solution requires embedding the discrete light source, such as an LED, into a centrally-located region in the second light guide. Light emitted from the light source enters and propagates to the edge of the second light guide, where the reflector reflects light emerging from the edge of the second light guide back into the edge of the first light guide. Optical elements that increase in density from the edge to the center of the first light guide redirect the light to emit at a substantially uniform intensity from the surface of the first light guide. However, sandwiching a light-confining interface layer between multiple light guides operates contrary to the objectives of constructing a low profile luminaire and minimizing design and manufacturing complexity.
U.S. Pat. No. 6,647,199 to Pelka at al. discloses a low profile lighting apparatus that includes a light guide coupled to a light source for injecting light into the light guide. In one embodiment, multiple light sources surrounded by diffusive reflective material may introduce light at spaced peripheral locations along the edge of a rectangularly-shaped light guide. However, because the majority of light injected into the edge of the light guide originates from directional-light generating LEDs, a complex plurality of display elements must be designed into the light guide to shape light propagating through the light guide into a substantially uniform illumination profile.
Accordingly, and with the above in mind, a need exists for a low profile luminaire that may be employed within the volume of space available in an existing canister light fixture, and that efficiently delivers improved lighting quality compared to traditional lamps. More specifically, a need exists for a canister-based lighting solution that may benefit from the advantages of digital lighting technology, while exhibiting a more uniform illumination profile than legacy downlight solutions. Additionally, a need exists for a luminaire designed for ease of installation as well as for manufacturing cost reduction.
This background information is provided to reveal information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.